Display screen or portion thereof with transitional graphical user interface



FIG. 1 is a first image in a sequence for a display screen or portion thereof with transitional graphical user interface showing our new design;

FIG. 2 is a second image thereof; and,

FIG. 3 is a third image thereof.

The broken lines at the outer perimeter of the figures depict a display screen or portion thereof and form no part of the claimed design. The remaining broken lines in the figures depict portions of the graphical user interface that form no part of the claimed design.

The appearance of the transitional graphical user interface sequentially transitions between the images shown in FIGS. 1-3. The process or period in which one image transitions to another forms no part of the claimed design. 

CLAIM The ornamental design for a display screen or portion thereof with transitional graphical user interface, as shown and described. 